Fig. 2.

Molecular modules for specifying spikelet identity and floret fertility. Spikelet arises from the spikelet meristem, which is derived from inflorescence or branch meristem. The “florigen activation complex” (FAC) complex integrates environmental and genetic signals to promoter flowering and inflorescence development. Phytohormones such as CK and auxin play important roles in maintaining meristem activity and primordium emergence. The FT-TFL, AP1/FUL and SEP-like MADS TFs interact antagonistically or in parallel with each other to establish IM and BM identity, while BR might restrain expression region of boundary genes to establish spikelet identity. Early expression of such boundary genes might confer “unbranch”-spike architecture. The phytohormone JA plays important role in floret fertility, and this pathway could be utilized in increasing floret number. BM branch meristem, BR brassinosteroid, CK cytokinin, FAC florigen activation complex, IM inflorescence meristem, SpM spikelet meristem. See also Table 1 and Box 1 for further explanations